Use the justify-content-center
helper class on the form
. That will center the contents with the flex property justify-content: center;
#home{
background-image: url('../img/jumbotron-bkg-2.jpg');
margin-top: 50px;
text-align: center;
}
<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet"/>
<div class="jumbotron" id="home">
<h1 class="display-3">My Awesome App!</h1>
<p class="lead">This is why you should download this fantastic app!</p>
<hr class="my-4">
<p>Want to know more? Join our mailing list!</p>
<form class="form-inline justify-content-center">
<label class="sr-only" for="yourEmail">Email</label>
<div class="input-group mb-2 mr-sm-2 mb-sm-0">
<div class="input-group-addon">@</div>
<input type="text" class="form-control" id="yourEmail" placeholder="Your Email">
</div>
<button type="button" class="btn btn-primary my-2 my-sm-0">Sign Up</button>
</form>
</div>